Having organized homes for adult children with elderly parents, our opinion is that one of the worst thing an adult child can do for his/her parents is to buy things for them. Unless an item is really broken (e.g. washing machine, TV, juicer), or something they've said they'll need, refrain from buying things (physical objects) for them. Because it'll end up as clutter in their homes.
Many elderly folks have lived through frugal times and will often not let go of an old item while it is still usable. Unless the new item is one that they can use in their daily lives, and you can physically install it in place for them, and remove the old item, the elderly will not put the new items to use.
The worst things are souvenirs, food items that they are not familiar with or do not particularly desire, houseware like plates, cups, vases, etc. They will clutter up the elderly folks' homes.
Instead, take them out for a meal, for a short vacation, for a cruise, for a BBQ, or even to watch a concert. Give them the gift of your time - because that matters more than all the things you can buy for them.
If you're searching for the perfect gift that won't end up as clutter, click here for some ideas.